1. Field of the Invention
The present invention is related to the field of communications through networks, and more specifically to a unit and a method for rearranging bits in data words for compatibility among different data formats, and software for enabling the same.
2. Description of the Related Art
Integrated Services Digital Networks (ISDNs) are used for the transfer of data between different users. At the local level, this is accomplished by using ISDN Digital Signal Loop (IDSL) devices, such as IDSL modems.
In communications at the rate of 144 Kbs, a collection of 18 bits defines one word. These 18 bits belong in two channels, namely the B-channel (Berr) and the D-channel. Each data word has four segments, two in the B-channel, and two in the D-channel. Each of the first two segments, B1 and B2, has eight B-channel bits. Each of the second two segments, D1 and D2, has 1 D-channel bit.
A problem is that there exist two different methods, or formats, for sending each word. These two formats are now described.
Referring now to FIG. 1, the first format is also known as BBDD. As can be seen, the four segments of the word are transmitted in the sequence B1 B2 D1 D2. In the second format, also known as BDBD, the four segments of the word are transmitted in the sequence B1 D1 B2 D2. The difference in formats developed because the D-channels were often not used for signaling in ISDN. As such, since Time Domain Multiplexing (TDM) requires that the D-channel bits be included, they started being used for data bits for higher efficiency. The additional use resulted in the development of the second format.
Each device is programmed to communicate in only one of the two formats. The difference in the formats renders devices incompatible with each other. The whole point of network communication is that any device should be able to exchange data with any other device in the network.
The present invention overcomes these problems and limitations of the prior art.
Generally, the present invention provides a method for rendering the data formats compatible with each other. In particular, the method of the invention interchanges the second segment with the third segment.
In addition, the invention provides a bit rearranging unit, that is placed in the path of the data. The bit rearranging unit receives a word, and retransmits it after interchanging the second segment with the third segment. This permits an operator to convert an associated network device, which operates in one of the two formats, to a device that instead operates in the other format.
Moreover, the invention provides a device that includes the bit rearranging unit. The device includes a controller, and memory with software made according to the invention. The software monitors whether received transmission is incompatible, and if so, directs the bit rearranging unit to switch formats.
The invention renders network devices compatible where they were previously not. In addition, the software permits the device to adapt to communication with the right one of the two data formats on the fly, without the intervention of an operator. This is especially advantageous for customer premise equipment (CPE), which is not easily accessible by servicing personnel.
The invention will become more readily apparent from the following Detailed Description, which proceeds with reference to the drawings, in which: